Phase transition and thermodynamic properties of CaF2 via first principles

The structural stabilities, phase transitions and thermodynamic properties of CaF2 under high pressure and temperature are investigated by first-principles calculations based on the plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of CaF2 under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. Our results demonstrate that the sequence of the pressure-induced phase transition of CaF2 is the fluorite structure (Fm3m), PbCl2-type structure (Pnma) and Ni2In-type structure (P63/mmc), and the transition pressures are obtained. The temperature-dependent volume and thermodynamic properties of Fm3m phase CaF2 at 0 GPa are presented. The thermodynamic properties of CaF2 in Fm3m, Pnma and P63/mmc phases at 300 K are predicted using the corrected and uncorrected quasi-harmonic approximation model. The variations of the thermal expansion α and heat capacity CV with pressure P and temperature T of CaF2 in the three phases are systematically obtained.